Various methods for molding hollow containers composed of resin materials have been proposed so far. A typical method of them is an injection blow molding method which comprises forming a preform (parison) by injection molding, and blow molding this preform to form a hollow container.
An injection blow molding apparatus adopting this injection blow molding method has an injection molding section equipped with an injection device (injection unit) and an injection mold, and a blow molding section equipped with a blow molding machine and a blow mold. In the injection molding section, a resin material is injected by the injection device into the injection mold to form a preform. In the blow molding section, the preform accommodated in the blow mold is blow molded by the blow molding machine to form a hollow container. Such an injection blow molding apparatus is called, for example, a one-stage or hot parison injection blow molding apparatus.
The injection blow molding apparatus generally moves the injection mold and the blow mold by actuators composed of hydraulic cylinders or the like to carry out mold clamping. Each actuator is supplied with oil from an oil tank by a hydraulic drive source which has a plurality of, for example, 2 to 3 fixed pumps and one induction motor. In recent years, injection blow molding apparatuses have appeared which reduce energy consumption during molding, for example, by adopting a hydraulic drive source including one or two variable pumps, which have been changed from the two to three fixed pumps, and an induction motor combined therewith. However, a further improvement in the energy saving properties of the injection blow molding apparatus is desired.
To meet such a desire, a proposal has been made for an injection device (injection unit) constituting an injection molding apparatus, the injection device having, for example, a hydraulic drive source which includes a fixed discharge hydraulic pump and a drive motor (e.g., servo motor) for driving this hydraulic pump, and which controls the rotational speed of the drive motor to control the discharge flow rate and the discharge pressure of the hydraulic pump (see, for example, Patent Document 1).